Separate long/lat columns for multilinestrings and plotting in colours

Question

I am new to plotting in R/leaflet. I am plotting a shapefile with multilinestrings into R with leaflet. Is there a way I can extract from the geometry column separate columns for lat and long coordinates? I have looked at this answer and this one, but I can't get the right result and it's a mixture of long/lat co-ordinates in each column.

The end result I would like to get is a map where the lines are coloured based on a variable (like this), but in order to run the loop I need to have long/lat co-ordinates separated.

Answer 1

I have two comments: to export lat & long coordinates of a multilinestring you could use sf::st_coordinates(), provided your multilinestring is in an unprojected CRS (otherwise you would get eastings & northings instead).

But I believe that - provided that I understand your question correctly - you are making it unnecessarily complicated.

Color coding multilines based on a variable can be done by the means of leaflet::colorFactor(). You first declare a palette by the means of a named lookup table - linking values to colors - and then apply it in your leaflet::addPolylines() call.

To illustrate on an example consider this piece of code; as your shapefile is not reproducible I am using a dataset of 13 rivers from Natural Earth to get a multiliestring (any multilinestring).

library(rnaturalearth) # to get some multilinestrings / any multilinestrings :)
library(dplyr)
library(sf)

rivers <- ne_download(category = 'physical', 
                      scale = 110, 
                      type = 'rivers_lake_centerlines',
                      returnclass = 'sf') %>% 
  mutate(color_source = case_when(name %in% c('Mississippi',
                                              'Peace',
                                              'Amazonas',
                                              'Paraná') ~ "Americas",
                                  T ~ "Rest of World")) %>% 
  group_by(color_source) %>% 
  summarise()
  
library(leaflet)

# prepare a palette - manual colors according to color_source column
palPwr <- leaflet::colorFactor(palette = c("Americas" = "red", 
                                           "Rest of World" = "blue"), 
                               domain = rivers$color_source)

# first prepare a leaflet plot ...
lplot <- leaflet(rivers) %>% 
  addProviderTiles("CartoDB.Positron") %>% # or any other basemap...
  addPolylines(color = ~palPwr(color_source), # note the tilde notation!
               opacity = 2/3) %>% # opacity = alpha
  leaflet::addLegend(position = "bottomright",
                     values = ~color_source, # data frame column for legend
                     opacity = .7, # alpha of the legend
                     pal = palPwr, # palette declared earlier
                     title = "Rivers of the World")

lplot #  ... then display it